The present invention relates to a braking system suitable for an aircraft and a method for the control of a braking system comprising a plurality of brake assemblies at least one of which is operable independently of the other or another of the brake assemblies. The invention relates also to a brake control system for the control of a plurality of carbon brakes and to a braking system such as an aircraft braking system comprising a plurality of carbon brakes and to a braking system such as an aircraft braking system comprising a plurality of carbon brakes rakes operatively associated with the brake control system.
The term carbon brake is used to mean a brake assembly having friction discs of a carbon-carbon composite material comprising a carbon fiber reinforcing material within a carbon matrix.
The ability to stop an aircraft both quickly and economically is of great importance and enormous amounts of kinetic energy have to be dissipated in order to bring a moving aircraft to rest, particularly in RTO (refused or rejected take-off) situation. The aircraft velocity may be decreased and the kinetic energy thereby dissipated by drag forces, by application of the engine thrust reversers and by application of the aircraft wheel brakes. The drag forces can be increased by deploying of airbrakes or speed brakes on the aircraft wings.
However, very high energy brake applications in an RTO situation are fortunately rare events and therefore play little, if any, part in determining overall brake operating economics.
It is now recognized that the rate of wear of carbon brake discs is not proportional to the energy dissipated during the time the brakes are applied, brake wear being disproportionately high when energy input to the brake is low. Consequently it is beneficial to apply only a restricted number of the available brakes when the required braking action is relatively low.
The concept of applying only limited numbers of brakes during taxiing operations but all the available brakes in a landing run has already been disclosed in GB 2216209B and U.S. Pat. No. 4,097,610. The concept has been described variously as brake disabling, selective braking or as taxi-brake select.
That concept has been developed by the teaching of GB 2289734 which describes a cascade operation. In the cascade operation the number of brake assemblies actuated is dependent on the pilot's pedal pressure demand and can increase, or decrease, as the pilot's demand increases or decreases.
In some circumstances a condition can arise in which it would be undesirable to employ or continue with selective braking, either simple selective braking as in GB 2216209 or cascade braking as in GB 2289734. Examples of conditions when simple selective or cascade braking might be undesirable include occasions when a skid condition is detected and when a hydraulic fuse has blown.